1. Field of the Invention
The present invention relates to a composite structure which comprises a metallic sheet and thermoplastic materials and a process for the production of said composite structure. In particular, the present invention is concerned with a composite structure which is well suited for use in a gasketed cover and the like used for housing electronic equipment. In the present invention, an injection molded thermoplastic material is integrated with a metallic sheet which is coated in advance with an adhesive, and a process for readily and efficiently producing said composite structure.
2. Description of the Related Arts
The development of electronic equipment in recent years is a cause for amazement. The previously mentioned equipment, which is subjected to printed circuit on a substrate by the use of integrated circuits utilizing semiconductors, is directed to compact, lightweight equipment which is prone to be readily damaged by moisture or dampness in particular. Accordingly, the hermetically sealing properties of a case housing electronic equipment is a factor of importance for the performance and durability of the electronic equipment.
The case housing electronic equipment constitutes a box body and a cover body, which are integrated by interposing on the joining surface thereof, a gasket made of vulcanized rubber, a urethane foam and a thermoplastic material. The gasket is fitted to a cover body and thus fixed to the cover, but there is unavailable a favorable method of adhesively bonding the gasket to the cover body. Accordingly, the adhesion is carried out by a (1) method comprising fixing the gasket on the cover body by means of a double-coated tape, or a (2) method comprising making holes in the cover body and fixing a gasket material from both sides of the cover body through the holes. The gasketed cover body is fixed on a box body by means of screws and accordingly, the fixing job is markedly facilitated by the adhesion of the gasket to the cover body.
As the above-mentioned first method, there is usually adopted a method in which a sheet like gasket material to which a double-coated tape is adhered is punched into the shape of a gasket, and the resulting gasket is fixed to the cover body. However, such a method is involved in such problems problematic in that most of the sheet-like gasket material after punching remains as waste material. Further, the production process is intricate or troublesome, thus inevitably increasing the production cost, since the gasket is fixed to the cover body after the gasket material has been punched into the requisite shape.
In the second method mentioned above, since the gasket material is exposed on the upper side of the cover body, it is sometimes upturned or curled when the cover body is inserted into the space of an electronic equipment main body. This space has been narrowing in recent years with the compaction of electronic equipment part items. Thus, such upturning or curling is responsible for defective sealing properties.
In addition, when the gasket which is fitted to a cover body is produced by such a method, and is used in a hard disc unit, it is impossible to suppress vibration due to the rotation of the hard disc.
The adhesion between a thermoplastic material and a metallic sheet such as the cover body is usually carried out by a method in which the thermoplastic material is subjected to adhesion treatment on the surface thereof by corona discharge or the like, and thereafter is stuck to the metallic sheet by using an epoxy-based or a urethane-based adhesive. However, such a method is intricate and troublesome and may involve gas generation. Thus, this method is inapplicable for a gasket used in electronic equipment.
In order to simply and facilitate the aforesaid job, consideration is given to a method comprising injection molding an adhesive thermoplastic material for the purpose of direct adhesion. However, such a thermoplastic material, even when being made rather hard, is enlarged upon injection molding, thereby making it impossible to employ the molded product as a gasket. Therefore, said method has not been adopted for production of a gasket for a cover body in a hard disc.
It is an object of the present invention to provide a composite structure which comprises a metallic sheet and a thermoplastic material which are adhered by injection molding. The resulting composite structure has excellent vibration-damping properties and is well suited for use as a gasket fitted to a cover body to be used for housing electronic equipment and the like.
Other objects of the present invention will become evident from the text of the specification hereinafter disclosed.
In view of the foregoing, intensive research and extensive investigation was conducted by the present inventors in order to develop the above-mentioned composite structure having favorable properties. As a result, it has been found that the general object can be achieved by a composite structure which is equipped, on a metallic sheet by coating, with a layer comprising a thermoplastic material capable of being thermally, fused adhered to a thermoplastic material to be placed thereon, and further equipped on said layer with a layer comprising a desirable thermoplastic material by means of thermal fusion adhesion. The present invention has been accomplished on the basis of the above-mentioned findings and information.
Specifically, the present invention provides a composite structure comprising a metallic sheet and two thermoplastic material layers which are integrated with each other. The first of the two thermoplastic layers comprises material capable of being thermally fusedly adhered with the second thermoplastic layer. The metallic sheet and the first thermoplastic layer are adhered to each other by coating, and the two thermoplastic layers are thermally fused adhered to each other. The present invention further provides a process of producing a composite structure which comprises installing, on a metallic sheet by coating, a layer (A) comprising a thermoplastic material capable of being thermally fused adhered to a thermoplastic material in a layer (B) to be placed thereon, and further installing the layer (B) on said layer (A) by thermally fusedly adhering a desirable thermoplastic material on said layer (A).